Hard to tell without seeing the condition of your frame. Like any problems with vehicles need to assess what caused the problem... was it near moist ocean area or snow area where they might have used salt clearing the road? Salt will eat metal and if your rust is caused by that then can have other areas to be concern. If nuts and bolts are badly rusted you need to buy Grade 8 bolts and nuts. If the rust isn't too bad, just clean with break cleaner and coat with oil. Be sure to check other areas under the car for rust areas. Sand rust off and with under coating paint, paint a couple of coating over.